1. Field of the Invention
The present invention relates to an image synthesizing device for receiving a plurality of images and outputting a synthesized image thereof.
2. Related Art
So-called a television conference system is known which makes communication by transmitting voice from a microphone, and camera images on a network, and outputting the images to a monitor and a speaker of the party. The simplest example is mutual communication between one terminal and another terminal, however, some television conference systems allow multiple points to communicate with one another at the same time.
When a multipoint television conference is held among a plurality of terminals, if full mesh type connection is used where all the terminals are simply connected to one another, traffic that flows through a network increases, and transmission/reception processing at the terminals, and accompanying encoding and decoding of voice and images increase, thus leading to inefficiency.
Consequently, a measures is usually taken in which a Multipoint Controller (MCU) is provided. An MCU is a type of server, and has functions of connecting to each terminal to receive and synthesize voice or images from each terminal, and send synthesized voice or images to each terminal.
With the MCU, each terminal needs only communicate with the MCU, and receive single synthetic voice and synthesized images from the MCU to obtain voice and images from all participants; therefore, efficiency increases in the terms of the above described traffic and processing amount at the terminals. In this way, an MCU serves an important role in a multipoint television conference, in which image synthesis technique is used.
Another application of image synthesis technique is a screen separation unit for a surveillance camera. Since a plurality of surveillance cameras are usually installed on a building, if the cameras are observed and recorded by separate monitors, large-scale equipment is needed, which is inconvenient. Therefore, a measures is usually taken in which a screen separation unit is used to synthesize a plurality of camera images into one image signal so that the signal may be verified by a single monitor and recorded by a single recorder. Image synthesis technique is also used for the screen separation unit.
Usually, although an MCU has a limit to the accommodations of terminals, if it desired to accommodate terminals beyond this limit, a cascade scheme is used in which an image originally supposed to be output to a terminal is connected with another MCU using multistage connection, as shown in FIG. 14. In FIG. 14, images from four terminals are synthesized at a first stage, MCU 1, and images from further three terminals are synthesized at a second stage, MCU 2; therefore, images from seven terminals in total are synthesized at the two MCUs 1 and 2. This configuration is described in e.g. JP-A 2000-253374 (Kokai).
Only one synthesized image is usually output at an MCU, however, configuration outputting a plurality of synthesized images is also proposed as described in JP-A 2006-222942 (Kokai). In this case, the multistage connection of MCUs is shown in FIG. 15. More specifically, the synthesized image of images input into one of MCU 3 or 4 is sent to another MCU 4 or 3 to share the input image between the MCUs 3 and 4, and, based on the input image, the MCUs 3 and 4 generate and output a plurality of synthesized images. This configuration is described in e.g. JP-A 08-88842(Kokai).
When a plurality of different synthesized images are output as described in e.g. JP-A 2006-222942, one MCU generates a final synthesized image by using the synthesized images output by another MCU, and synthesizing images from terminals which are connected thereto, however, the synthesized images input by the other MCU are treated as one image, therefore, the layout of each image cannot be changed. More specifically, in each synthesized image generated by the MCU, portions synthesized by the other MCU have the same synthetic layout, therefore, there is a problem that the degree of freedom of the synthesized images is reduced.